ComingSoon spoke with director Rob Marshall and was able to get some details about the first 3 acts of the movie:

"The whole opening and the first third of the film takes place in London. So we start on dry land and there is an impostor that Jack is looking for. He then escapes from the palace, gets captured by King George and there is a huge carriage chase…[W]e set sail and that is sort of the second act. It’s a new ship, Blackbeard’s ship, the ‘Queen Anne’s Revenge.’ Then Barbossa has a new ship called the ‘Providence.’ The third act is this incredible jungle adventure through caves where they are looking for the Fountain of Youth.”